Patent GB-681416-A (GB)
Title: Improvements in or relating to damping devices
IPC: F16F9/18
Filed: 1950-12-04
Abstract: 681,416. Dashpots ; hydraulic shockabsorbers. MERCIER, J. Dec. 4, 1950, No. 29682/50. Class 108 (iii). A hydraulic shock-absorber comprises a piston 2 defining chambers A, B, in a cylinder 1, passages 12, 13 connecting the chambers A, B having respective opposed one-way valves 10, 11, spring means 16, 17 associated with each valve and controlled by the piston position in the cylinder so that no damping occurs on movement of the pistons away from a normal equilibrium position (as shown), and a progressively decreasing damping effect occurs on the return stroke, and means 31 providing for displacement of liquid due to entry into the cylinder of the piston-rod 5. The springs 16, 17 also bias the piston to an equilibrium position. The piston-rod 5 has a lost-motion connection with the piston, the motion being damped by a dashpot formed by a head 34 carried by a stem 32 rigid with the rod 5. The latter extends with clearance through a shoulder 33 formed within a sleeve 30 rigid with the piston. Liquid flows to the reservoir 31 via valves 22 and a clearance 41. In modified constructions, Figs. 1 and 3 (not shown), the reservoir 31 is formed by a bellows extending between the end of the cylinder 1 and a head rigid with the piston-rod. In operation, the dashpot 33, 34 allows the piston-rod to adjust its position corresponding to the static load of the device. On downward movement of the piston from the equilibrium position, liquid flows up freely through the valve 10. On rebound the valve 10 is maintained closed and the resistance offered at any instant by the valve 11 is proportional to the displacement of the piston from the equilibrium position (due to its loading by the spring 17). On upward movement from the equilibrium position a similar action occurs, the valve 11 permitting free flow and the valve 10 controlling the rebound. An alternative form of relief valve 22 comprises a flexible metal blade, Fig. 2 (not shown), covering a port in the cylinder head. In the construction shown in Fig. 5, the reservoir is formed by the space between the cylinder 1 and an outer concentric cylinder 46. A spring-loaded relief valve 43 is provided between the cylinder and reservoir. Liquid can flow from the cylinder through a clearance between the piston-rod 5 and the cylinder head 8, and through passages 47 to the reservoir. In the construction shown in Fig. 6, the reservoir is provided by a bellows 7 which is in communication with the cylinder by a passage 49 in the piston-rod and a valve 50. An auxiliary reservoir 51 is connected with the cylinder by a flap valve 20 and a spring-loaded relief valve 22. Travel of the valves 10, 11 is limited by flanges 14, 15, and a Belleville washer may be disposed between the flange 14 and the valve 10. In the construction shown in Fig. 7, the valve 11 and associated spring are replaced by a valve 60 and Belleville type springs 62. The valve 60 controls flow through ports 61 leading from the chamber A to a reservoir 54. The valve 10 is acted on by a spring 56 and a weaker spring 55. The spring 56 at its upper end acts upon an apertured disc 57 which bears through pins 59 on the valve 60. The lower end of the reservoir is connected by ports 63 controlled by a spring-loaded flap-valve 64 with the lower end of the cylinder. The valve springs 10, 11 in each case may be homothetic with suspension springs or restoring forces operating in conjunction with the damper. Formulµ are derived for the duration of a complete oscillation of the damper and for the reduction in displacement of a spring suspension system incorporating the damper.